In the preparation and processing of film materials, such as photographic film and photographic paper, it is sometimes desirable to slightly wet the surface of the film, to modify an exisiting characteristic or aid in the creation of a new characteristic. The water is commonly supplied by a variety of means such as: dipping followed by squeegeeing or the like; blotting with a wet support; spraying, including ink jet spraying; rolling; "pulltruding" (low pressure die coating); or passing the film through humid air or steam and condensing water on the film. Many of these processes have the shortcoming of tending to be uneven in coverage. Wetting agents are commonly used to help overcome initial distribution inhomogeneities. The following references illustrate specific processes.
U.S. Pat. No. 3,470,625 discloses a process in which photographic paper is dried excessively, then a mixture of steam and air or inert gas are blown at one side of paper to humidify to an excess humidity, following which air at a desired paper humidity is blown at the other side of the paper.
U.S. Pat. No. 4,247,990 discloses a process for providing a uniform moisture content in a paper web by contact with a gas at a desired equilibrium moisture level.
U.S. Pat. No. 4,925,767 discloses a process for controlling the gloss of a hydrophilic colloid image by use of a wetted support.
U.S. Pat. No. 4,207,143 discloses a process for adding moisture to a web by emitting dry steam vapor from steamfoil nozzles and condensing vapor onto the web.
U.S. Pat. No. 3,838,000 discloses a process and apparatus in which humidified air is pulled through a web by suction. The humidified air is prepared by mixing air streams having different humidities. The patent states:
"The individual temperatures, relative humidities and action of the air streams may be varied to control the supply of moisture to the web 30. The system employs controlled precipitation of the moisture by adding two psychrometrically prepared air streams to effect precise availability of water mist in the air. As an example of the air streams that may be used, FIG. 3 shows two air streams of sufficiently different humidity to generate a mist. Three mixing lines are shown where 70.degree. F. saturated air is mixed with 174.degree., 165.degree. and 160.degree. saturated air. The saturated conditions are merely used as examples and, in actual practice, unsaturated air should be used to minimize dripping on the header surface prior to mixing." (col. 3, lines 59-7 1)
U.S. Pat. No. 3,720,150 discloses an apparatus in which diazo film is fed in through a slot, subjected to a recycled water vapor-air mixture to condense water onto the film and is simultaneously exposed to ammonia vapor, and then heated and fed out through a slot. The apparatus moves the air with a blower and includes a chamber containing a water reservoir.
It would thus be desirable to provide an improved apparatus and method for depositing a very small and uniform amount of water on a substrate.